Three's not always company.
After the date, they're on their own. Don't be dragged by one or both into serving as a go-between. Say, "I'm glad you liked him and I believe he had a good time as well but I'm not comfortable calling to insist he ask you out."
Don't take it personally.
If your friend rejects your choice, she's not rejecting you. Perhaps, you can use the feedback to find her a more appropriate match. If she rails at you for setting her up with a cretin, well, what you did was still a caring, wonderful gesture for which you'll win karma points. You'll also know from now on not to meddle in her love life.